Adjuvant for pharmaceutical preparations

A copolymer which comprises at least two structural units of the following formula (I'):

• ##STR8## wherein R is a divalent organic group and R.sup.1 is an oligosaccharide, wherein said oligosaccharide is unsubstituted or substituted with a moiety consisting of an acyl group, and has 2-10 saccharide residues, and is hydrolyzed and/or assimilated in the large intestine;
• and
• at least one structural unit of the following formula (II):
• ##STR9## wherein R is a divalent organic group, each of X.sup.1 and X.sup.2 is independently an oxygen atom, an imino group or a sulfur atom and R.sup.2 is selected from the group consisting of a saturated hydrocarbon having 2 to 20 carbon atoms, an unsaturated hydrocarbon having 4 to 20 carbon atoms, a polyalkylene, a polyalkylene glycol, a polyarylene oxide, a polyester and a polyamide when simultaneously R is phenylene and R.sup.1 has 2 saccharide residues, the ratio of I':II in the copolymer is greater than 10:90.